Printing quality issue...

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Recently I started having issue with some printing...I have been trying to understand the circumstances but could not find any correlation...For instance I print twice the same part with the same gcode and I have the issue only once !

It's a if the plastic was not sticking properly...You don't get a smooth surface as expected but a pile of filaments ! Here are a typical view :

Any idea ? I played on speed but it didn't change anything...

Thanks !

D

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What settings are you running? What filaments? It looks hot, I wouldn't expect to see layer droop like that unless I was way hot. Without knowing anything more of your settings, it's hard to say. Could always be the filament...did you change filament? Do you have pics of the other print?

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The printer can't print in mid-air - gravity will pull the filament down. That's the basic problem. The blue arrow points to an overhang that's about at 45 degrees. If you imagine the layer that sticks out the most being laid down - you can imagine that it's mostly over air but just barely attached to the layer below.

The red arrow points to a layer that was out over air. I imagine there was an overhang here.

One solution is to reduce your layer height. You have very thick layer heights (which makes for very fast printing!) but you get these "printing in air" issues. With a layer height half the nozzle width you can easily print 45 degree overhangs with perfect quality. It will print even with almost horizontal - up to around 70 degree's from vertical or 20 degrees from horizontal.

But with your roughly 1 to 1 nozzle width to layer height you can just barely print 45 degree overhangs.

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Actually looking at the photo one more time - it does look like massive overextrusion. On overhangs there is enough space for the high pressure filament to leak out all over the place but on most layers there just isn't enough space so the filament slips or grinds instead.

overextrusion can be caused by Z errors or E errors. If the Z axis isn't moving as far as expected you would also notice your parts are the wrong height. By like half. Are your parts half the height they were supposed to be? Make sure.

E errors - wrong steps/mm or accidentally set flow to 1000% or something. I would retract the filament until it's part way inside the bowden and then extrude exactly 10mm of filament (or say 25mm or 100mm) and then measure to see if it moved the right distance or instead what I expect to happen that it moves twice as far as expected.

If you have tinkerMarlin installed you can see this easily in the move menu.

Maybe you put the wrong firmware on the printer? The um2+ uses twice as many steps/mm versus the regular um2.